Fireworks projectiles are a category of firework articles. Fireworks projectiles are usually launched from a reusable launch tube. The fireworks projectile is a container loaded with fireworks effects, “special effects” like stars, comets, hummers, whistles etc. Fireworks projectiles come in many different shapes and sizes. They are manufactured with a propellant charge that is called a “lift charge” and which is attached to the projectile. Normally, the lift charge consists of a pressed, granulated and sieved fraction of black powder. Black powder, or sometimes called gunpowder, is a mixture of potassium nitrate (KNO3), charcoal and sulphur. Such a black powder charge propels the projectile into the air. When the black powder is ignited it burns very rapidly, so-called explosive burning or deflagration. During the explosive burning hot gasses are produced that enable the projectile to be launched from the launch tube.
Fireworks projectiles are usually made with a time-fuse, which serve as a time-delay element for explosion of the fireworks effects in the air. The time-fuse is ignited by means of the heat generated by the black powder, and after some delay it ignites the fireworks-effects inside the projectile in question which is located at the other end of the time-fuse, usually when the projectile is, after its launch, at its highest point, the so called “apex”.
A well-known characteristic of black powder is that it has a relatively high burn rate at low pressures.
A characteristic of fireworks projectiles and fireworks launch systems is that the fireworks projectiles may fit quite loosely inside the launch tubes. Hence, often there is a “clearance” between the projectile and the launch tube of a few millimetres or more. It is further observed that the launch tube is also typically made of relatively thin-walled materials, which also limit the maximum pressures that can be used. This combination of factors, i.e. high burn rate of black powder at atmospheric pressures, a clearance between the launch tube and the projectiles, and thin walls of the launch tubes, makes black powder the preferred propellant charge for fireworks projectiles.
The main problem of the currently available technology for launching fireworks projectiles is that black powder generates a lot of smoke as an undesired by-product when it burns. About half of the mass of black powder ends up as smoke, i.e. very small solid combustion products.
One possibility is the use of smokeless powder that is based on a nitrocellulose-based gun propellant material. However, smokeless powder needs a high pressure to ignite properly and burn rapidly. The simple replacement of black powder by a smokeless propellant material will fail to launch fireworks projectiles because pressures inside fireworks launch systems are too low to allow smokeless powders to ignite and burn properly. For instance, in U.S. Pat. No. 7,104,199 a system is described to launch fireworks shells or comets using a nitrocellulose propellant material. In said document it has been indicated that low temperature combustion of nitrocellulose provides sufficient force to propel solid pyrotechnic compositions from a launch tube to a desired apex, but that it lacks sufficient heat of combustion to ignite the compositions, their primes, or the delay fuses on aerial shells.
Other known techniques for launching fireworks projectiles involve techniques to employ compressed air. In this respect reference can, for example, be made to U.S. Pat. Nos. 5,627,338; 5,526,750; 5,339,741; and 5,282,455. The disadvantages of this system are, however, the high installation, operating and maintenance costs.